1. Field of the Invention
This invention relates to a rotor for a centrifuge, comprising bottom and top parts, which are formed with openings for receiving test tubes in rim engagement, wherein the bottom part is provided with a collecting trough which is constituted by an upwardly extending outer rim.
2. Description of the Prior Art
Such a rotor for a centrifuge is known from German Patent Specification 36 01 789. In the known design the bottom part has downwardly and outwardly extending receptacles for the test tubes. The receptacles are upwardly open and are also laterally open in an upward and outward direction so that the test tubes can be inserted into the receptacles from the outside in a lateral direction when the rotor is open and the test tubes are laterally guided. These lateral openings can be covered by the top part in that surface which contains the most outwardly disposed wall portion of the test tubes. The top part also covers the test tubes at their top end and also covers the bottom part.
Whereas that design affords certain advantages, the fact that the rotor consists of only two parts requires the test tubes to be inserted and held transversely to their longitudinal direction so that the two part has only a safety function. The top and bottom parts must be made to exactly fit each other and for this reason must be milled in time-consuming and expensive operations.
At operating speeds of an order up to 15,000 r.p.m., the interengaging sealing rims of the top and bottom parts will be subjected to considerable loads. The distribution of the support of the test tubes to the bottom and top parts results in uncertainties.
Published German Application 33 43 846 discloses for a centrifuge a rotor which has also laterally open receptacles for test tubes. But said receptacles are formed in a tripartite rotor having an insert in which the receptacles are open in a downwardly inclined direction and are adapted to be closed by a bottom part into which the insert can be inserted. The insert is held on the outside by a top part, which has a correspondingly inclined wall portion. That design is not only expensive but involves a difficult handling in use because the insert constitutes an intermediate or receiving part and is formed with the receptacles for the test tubes and must be held in an inverted position until the test tubes have been inserted. The test tubes can then be held in position in that the bottom part is applied from above. Thereafter the parts are inverted and inserted into the top part.
Published German Application 33 34 655 discloses a tripartite rotor comprising a bottom part, a tube-holding part and a top part. These three parts are all mounted on a drive shaft. The tube-holding part has an inwardly tapering, conical rim portion that is formed with receiving openings and at the rims of said openings is engaged by outwardly extending supporting rims of the test tubes. The tube-holding part has an outwardly inclined wall, which is so arranged and directed relative to the receiving openings that an intermediate portion of each test tube which has been inserted and which initially depends will engage that wall when the rotor is rotating at operational speeds.
The resulting subassembly is covered and held together by a top part which has been applied.
The bottom part comprises a collecting trough, which consists of an upwardly and inwardly deformed rim of the bottom part. The trough is covered by the rim of the tub-holding part. For this reason it is doubtful whether that collecting trough can fulfill its intended function because a breathing may occur between a lower rim flange of the tub-holding part and the collecting trough of the bottom part and may have the result that the contents of defective test tubes may be thrown out. Although the test tubes bear outwardly on the tube-holding part at and above a certain centrifuging speed, that contact is not uniformly effected but will depend on the volume of the contents of each test tube so that the test tubes may initially perform a pendulum motion and may rebound. This will impose a load on the rotor and requires the test tubes to be closed at their top by a cover to ensure that the contents cannot be thrown out. Problems are also be involved in the mounting and fixation of such cover because the test tubes are not firmly held in their receptacles.
GB A 2,098,516 discloses an integral rotor for a centrifuge, which rotor is provided with a detachable cover. The bottom part of the rotor is formed with the openings for receiving the rims of the test tubes and has an inturned bottom rim, which constitutes a collecting trough. That rotor constitutes a narrow double cone, which cannot easily be cleaned. Besides, the test tubes are held in the openings only at the top rim flanges of the tubes so that the latter are not reliably held in position. The walls of the test tubes cannot engage the outside surface of the bottom part so that the test tubes will swing in operation.
In the rotor disclosed in German Patent Specification 36 01 789 and GB A 2,098,516 the bottom part comprises a frustoconical wall portion for receiving the test tubes. In accordance with Published German Application 33 34 655 such wall portion is formed in an intermediate part.